My invention relates to a surge arrester and, more particularly, to a fragment resisting surge arrester core unit for installation in a surge arrester weather housing of elastomeric or other type of weather resisting material. Many varieties of surge arresters are known and are in use for connection in parallel with electrical equipment across a source of electrical power and the ground to shunt high current resulting from high voltage power surges such as those created by lightning. The shunting circuit of these surge arresters basically comprises an elongated, electrically conductive core between the terminal ends of which are contained a series of non-linear resistor elements, which commonly comprise metal oxide varistor blocks, stacked in series with or without intervening metal spacer heat sink blocks, a variety of electrical components, and one or more compression springs maintained in compression so as to maintain the core elements in electrical contact with each other. The electrically conductive core containing non-linear resistor elements is normally enclosed within an outer weatherproof housing commonly comprising various types of elastomeric material.
A long existing problem with surge arresters has been the explosive fragmentation of the core components due to the high pressures created by gases generated within the core by the passage through the core of high shunting currents when unusually high voltage surges are generated in the electrical power source by lightning or other phenomena. The high pressures generated within the core are caused by the heating of contained gases or air and the vaporization of the metal components of the core. The explosive fragmentation of the core ruptures the arrester housing and the hot fragmentations of the core components become widely scattered and often cause injuries to personnel or damage to equipment in the vicinity, in addition to being the source of fires.
Many solutions have been proposed and utilized to contain this explosive fragmentation of the arrester cores such as: installing reinforced metal bands around the outer weatherproof housing of the arrester; circumscribing the core varistor elements with heat conducting electrically insulating collars maintained in contact with the outer housing to dissipate the heat in the manner of U.S. Pat. No. 4,218,721; incorporating pressure relief diaphragms at the ends of the arrester cores in the manner of U.S. Pat. Nos. 3,727,108, No. 4,001,651, No. 4,240,124 and No. 4,404,614; encasing the arrester core of electrically conductive elements within a shell of high strength, fragment resistant, insulating material, such as resin impregnated fiberglass, in the manner of U.S. Pat. Nos. 4,404,614 and 4,851,955; enclosing the arrester core of electrically conductive elements within a spiral winding of highly tensioned, non-conductive filaments in a manner as places the respective portions of the arrester core under a high degree of axially directed compression in the manner disclosed in U.S. Pat. Nos. 4,656,555 and 4,905,118; enclosing the arrester core of electrically conductive elements within a rigid tube of high strength, insulating material having elongated regions of weakened areas extending longitudinally of the tube through which weakened areas high pressure gases generated by voltage surge created high shunting currents are vented in the manner of U.S. Pat. No. 4,930,039; enclosing the arrester core of electrically conductive elements in a jacket of plastic impregnated bi-directionally oriented weave fabric of which the greater strength strands of the biaxially oriented fabric extend longitudinally of the core and the lesser strength strands of the other orientation extend circumferentially of the core with a constrictive band compressively circumscribing the terminal ends of the core in the manner disclosed in my U.S. Pat. No. 5,047,891 in which the nature of the bi-directionally oriented fabric jacket opens longitudinally slits in the jacket when abnormally high pressures are generated within the core through which slits the internal gas pressure is vented before reaching destructive intensity.
As discussed at some length in my U.S. Pat. No. 5,047,891, incorporated herein by reference, the prior art core fragmentation resisting construction are deficient in establishing integrity of the core in the longitudinal direction, which deficiency the construction described in my aforesaid patent overcomes by the bi-directionally oriented weave fabric of the jacket having a higher degree of longitudinal tensile strength as compared to the lesser circumferential strength which results in slits opening longitudinally along the sides of the jacket through which high internal core pressures are vented. Although the longitudinally slitted fiberglass core enclosing jacket of U.S. Pat. No. 4,930,039 does provide means for venting high pressure gases generated in the core elements by high shunting currents, the slitted fiberglass jacket affixed at its ends to the core terminal ends is not a structure in which the vented jacket provides a high degree of longitudinal integrity to the core as would resist longitudinal explosion of the core. The manner by which the jacket is affixed to the core is deficient in shear strength.